In various industrial processes it is necessary to add measured increments of material at various stages of the processes. For example, in injection molding of plastics, colorant is added to produce colored products, in paint manufacture colorant is added to color paints, etc.. In other processes it is necessary to add lubricants, stabilizers, catalysts, etc.. Various spring-return valves have been used in the prior art to open and close ports to introduce the material into the process. These valves are power actuated in one direction and depend on spring return. The spring return has not proved entirely satisfactory as they can jam, weaken and break resulting in malfunction which causes scrap parts. Also these valves are not coordinated to actuate directly with the applied dispensing pressure so that delays in opening and closing occur and the desired accurate quantity of the material is not injected at the proper time.